Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules.

Naoual Allali,Manuel Dossot,Veronika Urbanova,Edward Mcrae,Brigitte Vigolo,Yves Fort,Sven Oberg,Xavier Devaux,Victor Mamane,Alexander V Soldatov,Chris P Ewels,Martine Mallet,Jean-Joseph Adjizian,Mathieu Etienne

doi:10.3762/bjnano.9.257

Abstract

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

Highlights

Carbon nanotubes (CNTs) have been recognized as interesting candidates for developing electrochemical sensors for almost two decades [1,2,3]
Carbonaceous impurities are mainly present in the form of carbon remains of nanometric size deposited along the CNT sidewalls and on the bundles but they are in very small amounts and the sample is clearly quite clean
We have shown that residual impurities in the case of mediated electron transfer play no role in the oxidation of nicotinamide adenine dinucleotide hydride (NADH), contrary to what has been presented in the literature for other systems

Summary

Introduction

Carbon nanotubes (CNTs) have been recognized as interesting candidates for developing electrochemical sensors for almost two decades [1,2,3]. The role of the PEG linker in the good electrochemical response was studied by molecular dynamics, which show that favorable interaction between the ETG units and water molecules prevents π-stacking of the ferrocene unit on the surface of the CNTs, allowing for a good electron transfer.

Results

Conclusion